Last week, I shared some of the mail I received from people who want to save big on groceries but who have an aversion to stocking up – even a little bit – during a good sale. Most often, the anti-stockpilers say they don't want to spend "extra money" to buy more products than they need for the current week.

The truth is, these same people overpay week after week for their groceries. This little-by-little overspending adds up to thousands of dollars. By contrast, shoppers who invest in groceries when they're on sale, using coupons to reduce prices further and stockpiling for future use, make the biggest returns.

One of my readers wrote to say that her first three months of Super-Couponing had been eye-opening. Instead of buying only what her family needs every week and buying only store-brand products, she now uses coupons, stocks up during sales, purchases name brands – and pays less for the name brands than the generics. These changes put an incredible $600 per month back into her family's budget:

"Our family just started Super- Couponing. We have completely changed our shopping and eating experience. We went from spending $250 a week to $100 a week, even with three children in diapers! We now eat a much greater variety of foods. Our former $250 a week was what we thought was bottom-of-the-barrel buying: only [store brands] and generics, minimal fresh produce. Now we enjoy baconwrapped filet, fresh produce every week and name-brand foods that we thought were just too fancy to spend ‘extra' on!"

Other readers write in to share their pleasure after tallying how much they've been able to save using coupons. This reader notes the incredible difference between sale prices and regular prices of the items she purchased during a nine-month period:

"I was a terrible shopper before and probably could not have told you how much I spent for a loaf of bread," she wrote. "Now, I know what prices things ‘should' be, and the couponing attitude has colored my whole shopping experience. I just spend less on everything. I've kept very good track because I like spreadsheets. Based on the regular [non-sale] price of items which I paid before without really noticing, we saved $9,000, or about 60 percent. I now have a small stockpile that could get us through a month or so if necesssary."

Another reader kept track of the coupons she used over the course of one year:

"I used a spreadsheet to document the items I was buying with coupons. I really wanted to see what my savings would be month to month. The total value of coupons I used in 2010 came out to $6,500 for my family of four. Simply amazing."

Remember, the most expensive time to buy something is when you actually need it. Think again about the shoppers who "don't want to spend any extra money" to buy more than they need right now. These people are overspending by thousands of dollars for the "convenience" of having less groceries on hand.

I'll leave you with one last e-mail from a reader who crunched the numbers on a single item to prove stockpiling is a good financial investment.

Canned vegetables are usually 85 cents each, he writes, but this week they are on sale for 70 cents. You decide to buy 24 cans, figuring you consume a can every other day for the next 48 days.

Instead of spending 85 cents for one can, you lay out $16.80 for 24 cans. The extra $15.95 is your "opportunity cost," the money you'll divert from other uses in order to purchase the extra cans. Extending this example to a full year, by stockpiling canned goods regularly, you'll save $3.60 every 48 days, or $27.37 a year. That's a 17.6 percent return on your $15.95, not to mention the money you'll save in gas by making fewer trips to the grocery store to stock up.

"The best part?" the reader asks. "When someone at a party brags about their stock investments, you can smile and say: "Gee, I stay clear of stocks, but I am earning a little over 17 percent in the commodities. And, of course, that's after taxes."

Jill Cataldo, a coupon-workshop instructor, writer and mother of three, never passes up a good deal. Learn more about couponing at her Web site, www.supercouponing.com. E-mail your own couponing victories and questions to jill@ctwfeatures.com.